“I think he has to be mindful that he does not have a full appreciation and understanding of what the implications are of going down that road,” Brennan told “Fox News Sunday.”

He also said that once Mr. Trump is inaugurated things will be different for him -- and that he’ll have responsibilities beyond just “talking and tweeting.”

“Now that he’s going to have an opportunity to do something for our national security as opposed to talking and tweeting, he’s going to have tremendous responsibility to make sure that U.S. and national security interests are protected,” Brennan said.

Brennan’s comments are indicative of just how much the relationship between Mr. Trump and the intelligence community has soured. Since the U.S. intelligence agencies announced in December that they had “high confidence” that Russia was working to influence the 2016 presidential election in his favor, Mr. Trump has expressed skepticism in their findings and publicly denounced the leaks from intelligence sources.

The president-elect took to Twitter Sunday evening to respond to Brennan, saying over two tweets, “Oh really, couldn’t do much worse - just look at Syria (red line), Crimea, Ukraine and the build-up of Russian nukes. Not good! Was this the leaker of Fake News?”

“The world is watching now what Trump says and listening very carefully,” he said. “If he doesn’t have confidence in the intelligence community, what signal does that send to our partners and allies as well as our adversaries?”

He said Mr. Trump needs to think and learn about an issue before he boldly professes his opinion on it: “Spontaneity is not something that protects national security interests,” he said.

And when it comes to Russia, Brennan said, any attempts to start over with Russia need to be handled very carefully.

“I think Mr. Trump has to understand that absolving Russia of various actions it has taken in the past number of years is a road that he needs to be very, very careful about moving down.”

Brennan’s comments echo those of other top intelligence officials, who say it’s no small thing to challenge the integrity of the country’s intelligence community.

Michael Morell, a former acting CIA director under President Obama, told CBS’ “Face the Nation” last week there would be “significant effects if the disparagement continues.”

Mr. Trump’s criticism is a “gut punch to people who go to work every day, nonpartisan, apolitical, trying to call it like they see it,” Morell said. “...It has undermined morale in the intelligence community and at CIA and that’s a big issue.”